Keyless router chuck

ABSTRACT

A tool receiver or chuck is provided which may receive a cutting tool, such as a router bit or the like, therewithin and non-rotatably retain the tool relative to a rotary driving device. The tool receiver includes a plurality of blades substantially encased within a conical surface. A biasing member biases the blades toward a narrow end of the conical surface such that the blades are biased in a tool engaging or operative position. The biasing member and conical surface thus bias the blades radially inward toward the cutting tool such that the blades engage the conical surface and the cutting tool. The tool receiver preferably includes a retaining member, which retains the blades within the conical surface and biases the blades radially outwardly toward the conical surface. The tool may be released by overcoming the biasing force of the biasing member by moving or sliding a retaining ring or by activating a lever or the like, such that no accessory wrenches or tools are required to insert or release a cutting tool or bit. Preferably, a width and radial length of the blades are dimensioned and/or the contact surfaces are defined to provide non-rotating engagement of the cutting tool by the blades, since the conical surface substantially limits twisting of the blades as the blades begin to rotate relative to the tool, thereby locking the tool relative to the blades. A ratio of the effective contact width of the blades to the radial length of the blades is preferably less than or equal to the coefficient of friction between each of the blades and the tool.

This application claims benefit of U.S. Provisional Pat. Application,Ser. No. 60/151,712, filed Aug. 31, 1999, which is hereby incorporatedin its entirety herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to drill or router chucks and,more particularly, to keyless router chucks.

Driving devices, such as drills or routers, include a tool retainerwhich non-rotatably secures a cutting tool, such as a drill bit or arouter tool, to the driving device. Rotation of a drive shaft of thedriving device then causes a corresponding rotation of the cutting tool.The clamping force of the retainer must provide sufficient grippingaction of the tool. Otherwise, if the gripping friction force isovercome, the tool will slip in its holder, which may result in poorperformance and hazard to those nearby.

Tool holding systems for woodworking, metalworking, and/or the like havebeen developed over many years. The most common types of tool holdersthat offer reasonable flexibility of gripping range are either colletsystems or chucks. Common applications for portable electric drillsincorporate keyless or keyed drill chucks. Within the metalworkingtrades such chucks are used for drills, while it is more common to seesplit steel collets for other applications such as milling or drillingwhere automated machinery is involved. These types of collets are inbroad use today. However, such collets require a substantial amount oftorque to be exerted on a threaded retainer in order to attainsufficient clamping force on the tool. This preloads the system suchthat the frictional engagement between the collet and the cutting toollimits rotational movement therebetween. In order to attain the hightorque necessary to achieve the necessary clamping force, typically theuser or operator uses wrenches or keys to rotate the threaded retainer,while holding the base or drive tool in a fixed position. Not only isthis process cumbersome and sometimes difficult, this also results inthe effective clamping forces being dependent on the torque applied bythe individual operator, which will vary from one person to another.

In some applications, blade type flexible collet chucks are utilized,which have radial blades that are forced into contact with the cuttingtool by the use of tapered cones and tightening nuts. Such collets arein use for light torque applications such as for tap holders and lightmachining, and are characterized by having substantially greatergripping ranges than the split steel types of collets. In mostapplications (except for keyless drill chucks), a tightening wrench orwrenches is necessary to cause the collet to grip the tool withsufficient force so that the friction between tool and collet issufficient to resist the forces of the application.

Collet closers have been proposed which provide for the sufficientclamping force by means other than using tightening wrenches. The colletmay be clamped via hand tightening of a threaded retainer on the drivingdevice. However, these collet closers have a very narrow grip range anda wide force requirement to successfully grip over this range.Accordingly, these may be ineffective for tools having a diameteroutside of the tight tolerance gripping range of the closers.Furthermore, these closers still require a high manual force to causethe collet to clamp onto the tool, which makes them difficult to use byan operator.

Existing collet systems of the split steel type and of the radial bladetype typically match the outside shape of the collet system to that ofthe cone within which it is tightened. This approach is consistent withthe desire to maintain wear resistance on the surfaces that grip thecollet by providing large contact surfaces. In the case of the bladetype collet chucks, the result of this design practice is to cause theblades to undergo a skewing tendency when the blade is in contact withthe tool. This skewing action tends to negate the gripping force systemof these designs because it forces the geometry into a violation of thedesign ratios necessary for the force system to work.

Therefore, there is a need in the art for a keyless chuck which mayreceive and non-rotatably retain a cutting tool, such as a router bit orthe like, therewithin, with minimal force required by an operator of thedriving device.

SUMMARY OF THE INVENTION

The present invention is intended to provide a keyless tool receiver orchuck, which is adaptable for use with a powered driving device ordriver, such as a router or the like. The tool receiver is biased in anengaged position by a biasing member, whereby an operator may insert acutting tool or bit within the receiver or release the tool therefrom byovercoming the biasing force of the biasing member. The tool receiverincludes a plurality of blades which are biased in the engaged positionwhereby the blades contact a conical surface of the driver along oneside and the cutting tool along the other side. The blades preferablyhave specific design ratios to further enhance the gripping of the toolby the tool receiver.

According to an aspect of the present invention, the tool receiver isadapted to non-rotatably secure a tool at a driving device. The toolreceiver is positioned within a tapered or conical surface of thedriving device. The conical surface has a narrow end and a wide endopposite the narrow end. The tool receiver comprises a plurality ofblades and a biasing member. The blades are positionable in a generallycircular manner at the conical surface and define a generally circularopening. The biasing member is adapted to bias the blades toward thenarrow end of the conical surface such that the blades are biased in theretaining position by the biasing member. The blades are adapted tonon-rotatably secure a tool with respect to the blades and the conicalsurface. Preferably, the tool receiver further includes a retainingmember which retains the blades and preferably biases the bladesradially outward toward the conical surface.

In one form, each of the blades has a thickness and a radial length. Aratio of the thickness to the radial length of each blade is preferablyno greater than a coefficient of friction between each of the blades andthe cutting tool. Preferably, a ratio of an effective contact width ofthe blades to the radial length of the blades is less than thecoefficient of friction between each of the blades and the cutting tool.Each of the plurality of blades has a tool engaging surface and a coneengaging surface opposite the tool engaging surface. The tool engagingsurfaces are adapted to engage a shaft of the tool, while the coneengaging surfaces are adapted to engage the conical surface of thedriving device. Preferably, the tool engaging surface of each blade hasa thickness which is greater than a thickness of the cone engagingsurface of the blade. Preferably, the tool receiver further includes apositive stop member which is adapted to limit insertion of the toolwithin the circular opening defined by the blades.

According to another aspect of the present invention, a tool receiverfor non-rotatably securing a tool to a driving device comprises aplurality of blades, a conical member and a biasing member. Each of theblades has a tool engaging surface and a cone engaging surface oppositethe tool engaging surface. The conical member at least partially encasesthe blades and biases the blades radially inward toward a circularopening defined by the tool engaging surfaces of the blades. The conicalmember defines a tapered or conical surface which has a narrow end and awide end opposite the narrow end. The conical member is rotatablydrivable by the driving device. The blades are positionable in agenerally circular manner within the conical member whereby the toolengaging surfaces of blades define a generally circular opening. Thecone engaging surfaces engage the conical surface of the conical member.The biasing member biases the blades toward the narrow end of theconical surface such that the blades are biased in a retaining positionby the biasing member and the conical member. The tool receiver isadapted to non-rotatably secure the tool with respect to the blades andthe conical member at the tool engaging surfaces of the blades.

Preferably, the tool retainer includes a retaining member which retainsthe blades in the generally circular manner within the conical member.The retaining member is flexible to allow pivotal movement of the bladeswithin the conical member with respect to the tool and the conicalmember. The pivotal movement is limited by the tool engaging surfacesengaging the tool and the cone engaging surfaces engaging the conicalmember, since a diagonal radial dimension of the blades is greater thanthe distance between the tool and the conical surface, which furtherlimits rotation of the tool relative to the blades. Preferably, theretaining member biases the plurality of blades radially outward towardthe conical member. Preferably, the biasing member is releasable toallow the blades to move toward the wide end of the conical surface,such that the tool engaging surfaces define a larger opening forreceiving a tool therewithin or for releasing a tool that is alreadypositioned within the opening. Preferably, the biasing member isreleasable via a lever, which is movable to overcome the biasing forceof the biasing member.

According to another aspect of the present invention, a tool receiverfor non-rotatably securing a tool therewithin comprises a plurality ofblades and a conical member. Each of the plurality of blades has athickness and a radial length extending radially from a generallycircular opening defined by the plurality of blades. The conical memberis adapted to be rotatably driven by the driving device. The conicalmember at least partially encases the blades and biases the bladesradially inward such that when a tool is positioned at the opening, theplurality of blades are adapted to engage the conical member and thetool. A ratio of the thickness to the radial length of the blades is nogreater than a coefficient of friction between each of the plurality ofblades and the tool. Preferably, a ratio of the distance between a pointof contact of the blade on the tool and a line between the pivot pointand tool center to the radial dimension from the contact point and thepivot point is less than approximately the coefficient of frictionbetween the blade and the tool.

In one form, the tool receiver further includes a biasing member whichbiases the blades in an engaging position whereby the blades are adaptedto non-rotatably retain the tool within the conical member. Preferably,the tool receiver further includes a retaining member which retains theblades within the conical member and biases the blades radially outwardtoward the conical member.

Therefore, the present invention provides very high grip strengths whichrequire relatively low actuating forces and thus facilitates removal andreplacement of tools without the use of accessory wrenches or keys. Thebiasing member biases the tool receiver in an engaged position such thatwhen a tool is inserted within the receiver, the operator only has torelease the biasing member to lock the tool within the receiver. Thegripping blades lock the workpiece or tool in a manner so that higherloads on the tool caused by its working action result in naturallyhigher gripping forces. Because of the design ratios involved, it ispossible to initiate the gripping action with relatively small forces,thus obviating the need for tightening wrenches. Preferably, the currentdesign limits the contact zone of the blades to the conical surface toalso overcome the tendency of the blades to skew in the gripping coneand thus protects the geometry and force system.

These and other objects, purposes, advantages and features of thisinvention will become apparent upon review of the followingspecification in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation of a tool receiver in accordance with thepresent invention as mounted on a driving device;

FIG. 2 is an end elevation of the tool receiver of FIG. 1;

FIG. 3 is a sectional view of the tool receiver taken along the lineIII—III in FIG. 4;

FIG. 4 is a sectional view of the tool receiver taken along the lineIV—IV in FIG. 3;

FIG. 5 is a side elevation of a blade useful with the present invention;

FIG. 6 is an end elevation of the blade of FIG. 5;

FIGS. 7A-7E are end elevations of alternate blades designs which areuseful with the present invention;

FIG. 7F is an end elevation of a blade useful with the present inventionas it engages a conical surface of the driving device and a cuttingtool;

FIG. 8 is an end elevation of a retainer useful with the presentinvention;

FIG. 9 is a sectional view of the retainer, taken along the line IX—IXin FIG. 8;

FIG. 10A is a side elevation of the tool receiver of the presentinvention with a lever mounted to the driving device to release the toolreceiver;

FIG. 10B is an end elevation of the tool receiver of FIG. 10A;

FIG. 11 is a partial sectional view of an alternate embodiment of a toolreceiver in accordance with the present invention;

FIG. 12 is a partial sectional view taken along the line XII—XII in FIG.11;

FIG. 13 is a perspective view of a blade useful with the presentinvention; and

FIG. 14 is a perspective view of a cone engaging surface of a bladeuseful with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now specifically to the drawings and the illustrativeembodiments depicted therein, a tool receiver or chuck 10 is mounted toa driving device 12 and functions to receive a generally cylindricalshaft 14 a of a cutting tool 14 therewithin (FIG. 1). Tool receiver 10includes a plurality of blades 16 and a biasing member 18 (FIG. 3),which biases the blades in an engaged position for non-rotatablysecuring the tool 14 within tool receiver 10. The driving device 12includes a conical portion or tapered or conical member 20, whichdefines a conical or tapered surface 22 therewithin (FIG. 3). Conicalsurface 22 includes a narrow end 22 a and a wider end 22 b oppositenarrow end 22 a. Conical portion 20 is rotatably driven by drivingdevice 12. Conical surface 22 functions to bias blades 16 radiallyinward toward and into engagement with shaft 14 a of tool 14 in responseto biasing member 18 biasing the blades 16 toward narrow end 22 a ofconical surface 22. Driving device 12 may be any known rotatably drivendevice, such as a drill, router or the like. The tool receiver of thepresent invention is especially applicable to driving devices whichdrive tools or bits which have a specific and narrow diameter range.Preferably, tool receiver 10 includes six blades 16 positioned andspaced uniformly about the conical surface. However, more or less bladesmay be implemented, without affecting the scope of the presentinvention.

Tool receiver 10 may be mounted to a conventional driving device 12 viaany known means. Tool receiver 10 includes a body portion 24 which mayreadily engage an outer surface 20 a of conical member 20 to secure toolreceiver 10 to driving device 12 (FIGS. 1 and 3). Body member 24 is agenerally hollow member and includes a hexagonal nut portion 24 b andmay include an outer cylindrical portion 24 c. Nut portion 24 b issecurable to driving device 12, such as via threaded engagement of thenut portion to a threaded portion 21 of the driving device. Cylindricalportion 24 c of body member 24 extends longitudinally outwardly from nutportion 24 b and driving device 12 and defines an inner cylindricalsurface 24 d which extends longitudinally from outer or wider end 22 bof conical surface 22 of conical member 20. Body member 24 also providesan annular reaction surface 24 a positioned at an outer end ofcylindrical surface 24 d and radially inward from cylindrical portion 24c for engagement with biasing member 18, as discussed below.

Biasing member 18 is positioned between reaction surface 24 a of body 24and a spacer or washer 44, and functions to exert a force to push spacer44 longitudinal inwardly along surface 24 d toward narrow end 22 a ofconical surface 22. Biasing member 18 may comprise any known biasingmeans, such as coil spring 18 or a conical washer 118 (FIG. 11), wavewasher, finger spring, or any other means for providing a biasing forcebetween reaction surface 24 a of body 24 and spacer 44. The spring forceexerted by biasing member 18 may be selected for the particularapplication of tool receiver 10. The force selected must be sufficientto move the blades 16 into the engaging or operative position andcountermand the axial effect of the centrifugal force acting on theblades when the driving device is operated, while being low enough toallow an operator to overcome the biasing force to release the tool fromthe blades, as discussed in detail below.

Spacer 44 comprises a flat, circular ring or washer which is positionedaround blades 16 and between a biasing surface 16 a of blades 16 andbiasing member 18. An outer edge or surface of spacer 44 slides withinand along inner cylindrical surface 24 d of cylindrical portion 24 c ofbody member 24, to guide the longitudinal movement of blades 16 alongconical surface 22 of driving device 12.

Tool receiver 10 further includes a pull ring or releasing member 28,which is positioned at an outer end 10 a of tool receiver 10 and engagesa releasing surface 16 b of each of blades 16. Releasing member 28 islongitudinally movable with respect to body 24. As best shown in FIGS.1-3, pull ring 28 includes an outer ring 28 a and an inner cap 28 b. Cap28 b includes a longitudinally extending portion 28 c which is slidablealong an outer surface 24 e of cylindrical portion 24 c of body member24. Longitudinally extending portion 28 c may be cylindrical touniformly engage cylindrical portion 24 c of body member 24, or mayotherwise be correspondingly formed with portion 24 c. For example, bothportion 24 c and portion 28 c may comprise a hexagonal or othernon-cylindrical form, to allow longitudinal movement of releasing member28 along body member 24, while also limiting rotation of releasingmember 28 relative to body member 24, without affecting the scope of thepresent invention. Preferably, cap 28 b defines an opening 29 at acenter region thereof. As best seen in FIG. 2, opening 29 is generallycircular and preferably includes a plurality of tapered slots 29 a forreceiving an outer end 16 d of blades 16, in order is assist inalignment of the blades 16 within tool receiver 10. When inserted inslots 29 a, releasing surfaces 16 b of blades 16 engage an outer surface28 d of pull ring 28, such that longitudinal movement of pull ring orreleasing member 28 in an outward direction away from body 24 anddriving device 12 causes a corresponding longitudinally outward movementof blades 16 toward wider end 22 b of conical surface 22 and against thebiasing force of biasing member 18 via spacer 44, thereby releasing thetool from blades 16, as discussed in detail below.

Referring now to FIGS. 5 and 6, each of blades 16 includes a coneengaging surface or edge 17 a and at least one tool engaging surface oredge 17 b. Cone engaging surface 17 a is angled relative to toolengaging surface 17 b and corresponds generally to the angle of conicalsurface 22 of conical member 20, such that cone engaging surface 17 amay uniformly engage conical surface 22, while tool engaging surface 17b of each blade 16 is oriented generally parallel with the tool engagingsurfaces of the other blades. However, blades 16 may be otherwise curvedalong cone engaging surfaces 17 a to engage conical surface 22 at adesired point or region of blades, depending on the application.Optionally, cone engaging surface 17 a of blades 16 may be otherwiseformed to cooperate with conical surface 22 in an optimal manner,whereby the surfaces 17 a of the blades are formed to correspond withthe way the conical surface changes. For example, the cone engagingsurfaces 17 a may be tapered or angled to provide a more uniformgripping action between the blades and the tool shaft as the bladespivot. Preferably, the surfaces 17 a are formed relative to the conicalsurface such that the blades provide a linear edge of engagement withthe conical surface along the entire length of the cone engagingsurfaces 17 a of blades 16, as the blades pivot during operation of thedriving device. As shown in FIG. 14, this may be accomplished by formingthe cone engaging surface 17 a with a tapered edge which provides acentral edge or peak surface 17 f at one end (which is positioned towardthe narrow end of the conical surface) and a flattened portion 17 g atthe opposite end of the cone engaging surface (toward the larger end ofthe conical surface). The surfaces may be further curved or rounded,without affecting the scope of the present invention. A diagonal radialdimension R (FIG. 6) of blades 16 is selected which is greater than thedistance between a tool shaft and the conical surface. Therefore, as thetool resists rotation, the opposite surfaces of each blade are incontact with and wedged between the conical surface and the tool shaft,in order to securely grip the tool within the tool receiver, asdiscussed in detail below.

Preferably, tool engaging surface 17 b includes a pair of tool engagingsurfaces 17 c and 17 d. The tool engaging surfaces 17 c and 17 d arepreferably angled or flared in opposite directions with respect to oneanother, so as to engage shaft 14 a of tool 14 and prevent relativerotation of shaft 14 a in either direction. Preferably, one toolengaging surface 17 d, such as the inner surface is angled such thatnormal rotation of the driving device 12 causes a leading edge 17 e(FIGS. 4-6) of tool engaging surface 17 d to rotate in the drivendirection, thereby engaging shaft 14 a and forcing shaft 14 a to rotateas well. Angling of the blade in this manner substantially precludesslippage of shaft 14 a with respect to blades 16 in response to the toolencountering resistance to rotation as the driving device is operating.Additionally, a second tool engaging surface 17 c, such as the outersurface or edge, is angled in the opposite direction from tool engagingsurface 17 d, in order to prevent slippage or loosening of shaft 14 a ofthe cutting tool 14 when resistance to rotation of the tool is notpresent, such as when the tool is spinning freely or the driving devicehas been deactivated. Preferably, tool engaging surfaces 17 c and 17 dare angled slightly upwardly from a horizontal plane extending alongengaging surface 17 b, in order to provide opposite facing surfaceswhich engage the shaft of the tool as it may tend to rotate in eitherdirection, thereby further precluding slippage of the tool in eitherdirection relative to the blades.

As shown in FIGS. 7A-7C, the blades of the present invention may havevarious tool engaging surfaces 17 b for engaging the outer surface ofthe tool shaft 14 a. For example, engaging surfaces 17 b′ may besubstantially flat (FIG. 7A). Alternately, the tool engaging surfaces 17b″ may be generally squared such that the opposite angled or flaredsurfaces provide an oppositely raised or tapered engaging surface (FIG.7B). Additionally, the tool engaging surface 17 b″ may be curved toprovide a uniform curvature between the two engaging surfaces foruniformly engaging the outer surface of the tool shaft 14 a (FIG. 7C).Alternately, other edge or surface designs may be implemented, withoutaffecting the scope of the present invention.

Preferably, blades 16 are stamped or otherwise formed of steel and mayinclude a plurality of aperture or openings 16 e therethrough, in orderto reduce the mass of the blades and thus of the overall tool receiver.The blades may also be manufactured from a lighter material to furtherreduce the mass of the blades. By reducing the mass of the blades, thepresent invention thus reduces the centrifugal forces created byrotation of the blades. As shown in FIGS. 7D and 7E, the blades may beformed in various manners. For example, a blade 16′ may be formed byfolding the steel over, whereby one of the engaging surfaces 17 d′ isformed at one end of the material and the other engaging surface 17 c′is formed at an opposite end of the material, such that when thematerial is folded over, the tool engaging surfaces are generally sideby side one another (FIG. 7D). Preferably, blades 16 are formed suchthat the tool engaging surface or surfaces 17 b has a thickness that isgreater than the thickness of the cone engaging surface 17 a. Forexample, a blade 16″ may include a narrow cone engaging surface 17 a″and a wide tool engaging surface 17 c″, as shown in FIG. 7E. Thisprovides a wide contact surface of the blade to the shaft of the tool,while providing a narrow pivot surface of the blade at the conicalsurface of the driving device.

Preferably, the blade dimensions are selected such that the ratio ofblade thickness to a diagonal radial dimension of each blade is lessthan a coefficient of friction between the blade and the tool shaft.However, in order to account for curvature of the tool shaft, the ratiomay be modified. More particularly, the ratio of effective contact widthof the blade to radial length of the blade is preferably less than thecoefficient of friction between the blades and the tool shaft. Referringto FIG. 7F, the blade dimensions are more preferably designed andselected in a manner such that the equation D₁/D₂<f is satisfied;wherein D₁ is defined as the distance between the point of contact S ofthe blade to the tool shaft and a straight line L between pivot point Pand tool center C; D₂ is the radial dimension from the contacting pointof the tool surface S to pivot point P; and f is the coefficient offriction between the blade engaging surface 17 b and the tool shaft 14a. The blade to tool contact surfaces are selected and ground orotherwise formed to provide the specific rate of increase ofinterference between the blade and the tool shaft that is designed to benumerically less than the coefficient of friction between the materials,thereby substantially precluding the possibility of slippage of the toolshaft relative to the blades. This concept envisions rolling contactbetween the tool and the blades and not a static interface.

Preferably, blades 16 are retained in a generally circular manner withinconical member 20 by retaining member 26. As best shown in FIGS. 3, 4, 8and 9, retaining member 26 includes a plurality of blade retainers 27which include a pair of sidewalls 27 a and a base connector 27 b. Eachsidewall 27 a is connected to a sidewall 27 a of an adjacent bladeretainer 27 via a connection portion or ring 26 a of retaining member26. As shown in FIGS. 3 and 4, blades 16 are positioned within anopening 27 c defined in blade retainers 27, and base connector 27 bextends through a recess 16 f formed along tool engaging surface 17 b ofeach blade 16. Connecting portion 26 a of retaining member 26 extendsbetween the adjacent blade retainers 27 to maintain the blades in theproper orientation within and along conical surface 22. Alternately,portion 26 a of retaining member 26 may be a complete ring at the end ofthe blades toward the small or narrowed end of the conical surface,without affecting the scope of the present invention.

Preferably, tool retaining member 26 comprises a semi-rigid polymericmaterial, such as nylon or the like, which may be molded to the desiredform. Alternately, however, retaining member 26 may be formed from othermaterials, such as metal, plastic, rubber, or the like, withoutaffecting the scope of the present invention. Although retainer 26 issemi-rigid, blade retaining portions 27 preferably flex or pivotrelative to connecting portions 26 a to allow blades 16 to pivotslightly as they are engaged between the tool and conical surface.Because retaining member 26 functions to hold the blades substantiallystationary in their generally circular orientation with respect to oneanother, yet is at least partially deformable to allow the blades topivot slightly as they engage the tool shaft when the driving device isactuated, the retaining member may be substantially rigid and does nothave to be formed of a resilient rubber or plastic material as requiredby the collets of the prior art.

Preferably, tool receiver 10 further includes an outer seal portion 30positioned around blades 16 and within a recess 16 c formed in eachblade 16 (FIG. 3). Seal 30 preferably comprises a rubber like materialand is molded or otherwise formed to fit around each blade and around aninner surface 28 e of cap 28 b of pull ring 28, such that seal 30substantially surrounds the generally circular opening 32 defined by theblades 16 (FIGS. 1-3). Seal 30 provides a resilient surface 30 a forcutting tool 14 to rest against as the tool shaft 14 a of the tool isinserted into tool receiver 10, while also preventing contaminants, suchas dirt, shavings and the like, from entering tool receiver 10 when thedriving device is in use. Outer surface 30 a of seal 30 is preferablycurved to engage a curved, widening portion 14 b (FIG. 1) of cuttingtool 14, which is common on many conventional cutting tools and/orrouter bits.

Tool receiver 10 may further include a stop member 40 which may bepositioned at narrow end 22 a of conical surface 22 (FIG. 3). Stopmember 40 provides a positive mechanical stop of the shaft of the toolas the tool is inserted into tool receiver 10. The shaft 14 a of thetool is thus consistently inserted in an appropriate amount, therebyeliminating uncertainty and improving the safety of the system.Alternately, or in addition thereto, seal 30 may function as a stop toengage the outer, widened end 14 b of the shaft 14 a of a router tool toprevent over insertion of the bit. This is a substantial improvement,since over insertion of the tool results in the outer ends of the bladesengaging curved portion 14 b of shaft 14 a, which further results inuneven clamping of the shaft due to the wider diameter at the outer endof the shaft.

It is further envisioned that the region of contact between the bladeand the conical surface at which it acts may be modified to enhanceperformance and/or life cycle of the tool receiver and/or the drivingdevice. Such modifications may be desired in some circumstances, whereit may not be desirable to have the blades acting directly on theconical surface because of the wear that may be caused to the conicalsurface. In such situations the blades or tool retainer may include asmall wear pad or ring (not shown) which may be assembled to the bladesand thus spread the system loads over a wide area of the conicalsurface, while maintaining the essential geometry of the basicinvention. The wear pad or pads are preferably formed of steel or otherhard and highly durable material.

When positioned within the conical member 20 of the driving device 12,blades 16 are substantially retained by retaining member 26 in theirgenerally circular orientation. When pull ring 28 is pulled or otherwisemoved longitudinally away from driving device 12, blades 16 arecorrespondingly moved longitudinally outwardly, such that cone engagingsurfaces 17 a of blades 16 are moved toward wider end 22 b of conicalsurface 22. This allows the blades to move radially outwardly toincrease the gap defined between the engaging surfaces 17 b of theblades, and thus allow for insertion and/or removal of the cutting tool.Preferably, retaining member 26 functions to bias the blades 16 radiallyoutwardly, such that as the blades slide outwardly along conical surface22 toward wider end 22 b, the blades are biased to correspondingly moveradially outwardly to maintain engagement with conical surface 22. Thisensures that the gap or opening 32 defined by the engaging surfaces 17 bof blades 16 will increase as the blades 16 are pulled longitudinallyoutward from conical member 20 via longitudinal movement of pull ring28.

When pull ring 28 is released, biasing member 18 exerts sufficient forceto move blades 16 longitudinally inwardly toward narrow end 22 b ofconical surface 22 via spacer 44 at biasing surface 16 a of blades 16,such that cone engaging surfaces 17 a of blades 16 slide longitudinallyinwardly along conical surface 22 toward narrow end 22 a of conicalsurface 22. As the blades 16 slide along conical surface 22, bladeengaging surfaces 17 b are correspondingly moved radially inward toreduce the gap defined by the tool engaging surfaces, and thus engagethe shaft of the cutting tool and clamp or secure the tool within thetool receiver 10. After tool shaft 14 a is secured by tool engagingsurfaces 17 b of blade 16, driving device 12 may be actuated to rotateconical member 20, which correspondingly rotates body 24 and thus blades16. As the driving device operates and the cutting tool is engaged witha work piece, the system forces increase. As cutting resistance occurs,the tool resists rotation by the blades, such that the friction forcetends to pivot or rotate the blades about their opposite comers, whichare in contact with the tool and the opposite conical surface. As theforces increase, the blades will further pivot to further clamp orsecure the tool within the tool receiver. Accordingly, the greater theforce urging the tool to slip against the blade, the greater is theresultant force which causes the blades to grip the tool and thus resistslipping. The blades are designed such that as each blade pivots, thetool engaging surface 17 b clamps tighter on the tool shaft, since thetool engaging surface is preferably wider than a pivot edge along thecone engaging surface 17 a, which maintains engagement with conicalsurface 22 as the blades 16 pivot. The diagonal dimensions of the bladesthus defines the dimensional limit of the system beyond which the bladesmay rotate over center and lose their grip or clamp strength.

As shown in FIGS. 10A and 10B, tool receiver 10 may further include arelease lever 38, which provides enhanced mechanical advantage to anoperator to assist in overcoming the biasing forces of biasing member18. Lever 38 preferably includes a pair pivot points 39 at eitherdriving device 12 or body 24, a pair of releasing arms 40, which extendfrom pivots 39 to a cap or pull ring 28′, and a lever arm 42 extendingbetween pivots 39 and outwardly from tool receiver 10. Preferably,releasing arms 40 include a roller 41 rotatably mounted at an outer endthereof, whereby rollers 41 engage at a roller surface 28 a′ of cap orpull ring 28′. Lever 38 may be pivotally mounted at pivot axes 39 todriving device 12 or body 24 at a boss or other structure 39 a atdriving device 12 or body 24. As lever arm 42 is moved longitudinallyinwardly with respect to driving device 12 by an operator, releasingarms 40 pivot to push rollers 41 against roller surface 28 a′, whichcauses corresponding longitudinally outward movement of cap 28′ and thusof blades 16, in a similar manner as discussed above. Lever 38 thusprovides enhanced mechanical advantage to an operator, who may overcomethe biasing forces of biasing member 18 by simply depressing lever arm42 with one hand or even one finger or thumb. Although shown as a leverarm with rolling engagement with the cap or pull ring, clearly otherlevers or mechanical advantage mechanisms may be implemented to reducethe forces required to overcome the biasing member or otherwise to makethe tool receiver more ergonomically accommodating. For example, a leveror handle may cause rotation of a non-circular cam which rotates to movethe cap member to release the tool receiver, without affecting the scopeof the present invention.

Referring now to FIGS. 11-13, a tool receiver 110 is mountable to adriving device (not shown) and functions to non-rotatably receive a toolshaft therewithin. The driving device is preferably a router and thetool is a routing or cutting tool or bit for cutting wood as the tool isrotated at high RPMs by the driving device. However, the tool receivermay be used with other driving devices and may receive other tools, suchas drill bits or the like, without affecting the scope of the presentinvention. Tool receiver 110 includes a body 124 which is mountable tothe driving device and rotatably drives the components of the system.Tool receiver 110 further includes a housing 120 which includes an innerconical surface 122 which forcibly engages a plurality of blades 116 tothe shaft of the tool.

As discussed above with respect to tool receiver 10, blades 116 of toolreceiver 110 are radially dispersed around the centerline of the systemto engage the shaft of the tool uniformly around the shaft. The bladesare positioned relative to one another to define a generally circularopening for receiving the tool therein. Preferably, blades 116 aresubstantially similar to blades 16, discussed above, such that adetailed discussion will not be repeated herein. Suffice it to say,blades 116 include a cone engaging surface 117 a and at least one toolengaging surface 117 b opposite the cone engaging surface. Preferably,the blades are retained in their generally circular manner by aretaining member 126, which may be substantially similar to retainingmember 26, discussed above.

Housing 120 of tool receiver 110 includes a washer or ring 125 securedat one end of housing 120 toward base 124. A biasing member 118 ispositioned between ring 125 and a reaction or biasing surface 124 a ofbase 124 to bias the base 124 and thus the blades 116 toward a narrowend 122 a of conical surface 122, thereby forcing blades 116 into anengaged position for engaging and clamping the shaft of a tooltherebetween. Biasing member 118 may be any means for biasing, such as aconical shaped washer, which may flex to allow the system to bereleased, a coil spring or the like, similar to biasing member 18discussed above. Preferably, body 124, housing 120 and blades 116 areformed of steel or the like. Similar to retaining member 26 discussedabove, retaining member 126 is preferably formed of polymer material,such as nylon or the like, but may be formed of more rigid materials,such as metal or the like, without affecting the scope of the presentinvention.

The force system that is incorporated in the present invention ispreferably dependent on the creation of a specific limiting designratio. This limiting design ratio must exist with respect to thefriction properties between the gripping blades and the tool beinggripped. Simply put, the ratio of the blade thickness (t) (FIG. 13) toits radial dimension (rotational dimension) (r) (FIG. 13) is preferablyless than the coefficient of friction between the blade and the tool itis gripping. However, this equation may be modified to accommodate thetool curvature, as discussed above with respect to blades 16. It isfurther envisioned that the ratio may vary, and may even be greater thanor less than the coefficient of friction, depending on the curvatureeffect of the tool being gripped. Given this limiting geometricrelationship, the gripping force increases until the strength orgeometric stability of the system is overcome. If the ratio of bladewidth to radial dimension is greater than the coefficient of friction ofthe interface and curvature effect, then the progressive gripping forceof the present invention may not occur and gripping is then based on thefriction caused by the mechanical preload of the system.

Practical limits exist as to how small of a ratio of thickness to bladeradial dimension can be utilized. As the system forces increase, theparts necessarily deform and the blades begin to rotate about theiropposite comers. The diagonal dimension of the blades describes thedimensional limit of the system beyond which the system is unstable andloses grip strength because the blades may rotate over center. As bladethickness decreases, the cross comer dimension decreases and thus theamount of radial strain tolerance decreases. Similarly, as the radialdimensions of the blades increase, so does the tendency of the blades tobuckle, and the stiffness requirement of the housing is increased,requiring disproportionately thicker components. Moreover, longer radialdimensions create larger systems and greater material requirements. Itis thus preferred to reach a design compromise whereby the bladedimensional ratio remains below the friction coefficient yet the systemis of appropriate and workable dimensions.

In practice there may be occasions where the torsional load on theworking tool varies rapidly or even reverses direction. In order tomaintain grip control over the tool in such circumstances, the presentinvention utilizes the design ratio principle to maintain torsionalcontrol and utilizes friction to maintain axial control of the tool. Thetorsional control is enhanced by providing the second tool engagingsurface on the blades which is angled or flared in an opposite directionso as to maintain control or gripping of the tool when the tool reversesits rotational direction.

Therefore, the present invention provides a tool receiver fornon-rotatably securing a cutting tool, such as a router bit or the like,to a driving device, such as a drill, router or the like. The toolreceiver includes a biasing member which biases the receiver in anengaged position, such that the receiver may be easily used by anoperator and the tool may be inserted and removed without the use of anytools or keys. The tool receiver may further include a stop member tolimit axial movement of the tool within the receiver as the tool isinserted therein. The tool receiver preferably provides blades having aratio of width to radial length which provides improved gripping of thetool by the blades as the tool resists rotation.

The tool receiver of the present invention is adaptable for tool holdingapplications where it is desirable to change cutting tools without theneed for accessory wrenches and/or the like, and where large grippingforces are necessary. The tool receiver includes radially positionedblades which are retained by a retaining member or locating spring. Theblades are preferably of prescribed dimensional relationships andcircumscribed by a conical member. The conical member and/or the bladesmay be biased by an axial spring force to engage the conical member withthe radially outward edge of the blades and thus bias the bladesradially inward toward the centerline of the device. The blades may alsobe biased against the conical surface by the retaining member.

In order to release the tool from the tool receiver of the presentinvention, an operator simply applies pressure along the axis of thesystem in a longitudinal direction so as to collapse or otherwiseovercome the biasing member or axial spring, thus allowing the retainingmember to bias the blades radially outwardly from the tool, therebyreleasing the tool. A releasing member or pull ring positioned along theoutside diameter of the conical member preferably assists this action byproviding a smooth surface to which the operator may apply force. Inorder to further assist the operator, a lever system may be implementedwhich creates a mechanical advantage in overcoming the bias spring. Thislever system may be attached to the tool receiver or to the power toolon which the tool receiver is affixed.

The axial spring force is opposed by a body member which mounts the toolreceiver to a suitable power tool or driving device and transmits therotational driving force of the power tool. The driving force istransmitted to the conical member and thus to the blades. Rotation ofthe blades then causes corresponding rotation of the tool via thegripping action of the blades along the tool. As cutting resistanceoccurs, the tool resists rotation by the blades such that friction forcetends to pivot or rotate the blades about their opposite comers whichare in contact with the tool and the opposite conical surface. Whencertain dimensional ratios are maintained for the blades, the frictionforce causing rotation results in a camming effect which in turn resultsin an increase in friction force between the blades and the tool.Therefore, the greater the force urging the tool to slip against theblade, the greater is the force which causes the blade to grip the tooland resist slipping. The width and length of the blades and the diameterof the conical member are correspondingly selected such that the radialdiagonal length of the blades is greater than the distance between anouter surface of the tool shaft and the inner surface of the conicalmember. This substantially precludes rotation of the blades beyond aneffective range of operation. Alternative arrangements of the functionalcomponents can be devised to provide optimal solutions in givensituations.

The present invention thus eliminates the need for loose tools, such aswrenches, spindle locks, and the like, while changing router bits and/orother cutting tools. Because the pull ring and blades only slidelongitudinally with respect to the driving device, and do not requiresubstantial tightening via threaded engagement with the driving deviceto secure the tool therein, the tool receiver of the present inventionis less likely to seize in its locked position than are the currentsplit collet designs of the prior art. Additionally, because the tool ismoved into its locked position via releasing the receiving device,whereby the biasing member moves the blades into their locked position,the ability to securely hold the router bits is not dependent on theactions or ability of the operators, which results in improved overallsafety. The present invention may be adapted for use with existingdriving devices, such that the present invention is equally applicableas a retro-fit or aftermarket device and/or as an originallymanufactured component of the driving device.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the principles of the invention,which is intended to be limited only by the scope of the appendedclaims, as interpreted according to the principles of patent law.

The embodiments of the invention in which an exclusive property right orprivilege is claimed are defined as follows:
 1. A tool receiver adaptedto non-rotatably secure a tool at a driving device, said tool receiverbeing positioned within a conical surface of a driving device, theconical surface having a narrow end and a wide end opposite the narrowend, said tool receiver comprising: a plurality of blades which arepositionable in a generally circular manner at the conical surface andare adapted to engage the conical surface of the driving device, saidplurality of blades defining a generally circular opening which isadapted to receive the tool; and a biasing member which is adapted tobias said blades toward the narrow end of the conical surface such thatsaid blades are biased in a retaining position by said biasing memberand are adapted to non-rotatably secure a tool with respect to the saidblades and the conical surface when in said retaining position, each ofsaid plurality of blades including a tool engaging surface and a coneengaging surface opposite said tool engaging surface, said cone engagingsurfaces being adapted to engage the conical surface of the drivingdevice and said tool engaging surfaces defining said generally circularopening and being adapted to engage the tool, wherein said cone engagingsurface is formed with a tapered surface therealong to cooperate withsaid conical surface as said blades pivot during operation of thedriving device, thereby providing generally uniform engagement of saidtool engaging surface with the tool.
 2. The tool receiver of claim 1further including a retaining member which retains said plurality ofblades in the generally circular manner.
 3. The tool receiver of claim2, wherein said retaining member comprises a semi-rigid polymer.
 4. Thetool receiver of claim 3, wherein said retaining member comprises nylon.5. The tool receiver of claim 2, wherein said retaining member biasessaid plurality of blades radially outwardly.
 6. The tool receiver ofclaim 1, wherein said biasing member is deformable to allow said bladesto move to a released position whereby said blades are spaced apart toreceive a tool within said tool receiver.
 7. The tool receiver of claim6, wherein said biasing member is deformable via a lever.
 8. The toolreceiver of claim 1 further including a stop member which is adapted tolimit insertion of a tool within said circular opening of said toolengaging surfaces.
 9. The tool receiver of claim 1, wherein a tool isreceived in an opening at one of the narrow end of the conical surfaceand the wide end of the conical surface.
 10. A tool receiver adapted tonon-rotatably secure a tool at a driving device, said tool receiverbeing positioned within a conical surface of a driving device, theconical surface having a narrow end and a wide end opposite the narrowend, said tool receiver comprising: a plurality of blades which arepositionable in a generally circular manner at the conical surface andare adapted to engage the conical surface of the driving device, saidplurality of blades defining a generally circular opening which isadapted to receive the tool; and a biasing member which is adapted tobias said blades toward the narrow end of the conical surface such thatsaid blades are biased in a retaining position by said biasing memberand are adapted to non-rotatably secure a tool with respect to the saidblades and the conical surface when in said retaining position, each ofsaid plurality of blades including a tool engaging surface and a coneengaging surface opposite said tool engaging surface, said cone engagingsurfaces being adapted to engage the conical surface of the drivingdevice and said tool engaging surfaces defining said generally circularopening and being adapted to engage the tool, wherein said tool engagingsurface of each of said blades comprises first and second tool engagingsurfaces, said first tool engaging surface being angled in a firstdirection and said second tool engaging surface being angled in a seconddirection, said first direction being generally opposite to said seconddirection.
 11. A tool receiver adapted to non-rotatably secure a tool ata driving device, said tool receiver being positioned within a conicalsurface of a driving device, the conical surface having a narrow end anda wide end opposite the narrow end, said tool receiver comprising: aplurality of blades which are positionable in a generally circularmanner at the conical surface and are adapted to engage the conicalsurface of the driving device, said plurality of blades defining agenerally circular opening which is adapted to receive the tool; and abiasing member which is adapted to bias said blades toward the narrowend of the conical surface such that said blades are biased in aretaining position by said biasing member and are adapted tonon-rotatably secure a tool with respect to the said blades and theconical surface when in said retaining position, each of said pluralityof blades including a tool engaging surface and a cone engaging surfaceopposite said tool engaging surface, said cone engaging surfaces beingadapted to engage the conical surface of the driving device and saidtool engaging surfaces defining said generally circular opening andbeing adapted to engage the tool, wherein said tool engaging surface ofeach of said blades has a first width and said cone engaging surface hasa second width, said first width being greater than said second width.12. A tool receiver adapted to non-rotatably secure a tool at a drivingdevice, said tool receiver being positioned within a conical surface ofa driving device, the conical surface having a narrow end and a wide endopposite the narrow end, said tool receiver comprising: a plurality ofblades which are positionable in a generally circular manner at theconical surface and are adapted to engage the conical surface of thedriving device, said plurality of blades defining a generally circularopening which is adapted to receive the tool; and a biasing member whichis adapted to bias said blades toward the narrow end of the conicalsurface such that said blades are biased in a retaining position by saidbiasing member and are adapted to non-rotatably secure a tool withrespect to the said blades and the conical surface when in saidretaining position, wherein each of said blades has a thickness and aradial length, a ratio of said thickness to said radial length being nogreater than a coefficient of friction between each of said plurality ofblades and the tool.
 13. The tool receiver of claim 12, wherein each ofsaid plurality of blades includes a tool engaging surface and a coneengaging surface opposite said tool engaging surface, said cone engagingsurfaces being adapted to engage the conical surface of the drivingdevice and said tool engaging surfaces defining said generally circularopening and being adapted to engage the tool.
 14. A tool receiveradapted to non-rotatably secure a tool at a driving device, said toolreceiver being positioned within a conical surface of a driving device,the conical surface having a narrow end and a wide end opposite thenarrow end, said tool receiver comprising: a plurality of blades whichare positionable in a generally circular manner at the conical surfaceand are adapted to engage the conical surface of the driving device,said plurality of blades defining a generally circular opening which isadapted to receive the tool; and a biasing member which is adapted tobias said blades toward the narrow end of the conical surface such thatsaid blades are biased in a retaining position by said biasing memberand are adapted to non-rotatably secure a tool with respect to the saidblades and the conical surface when in said retaining position, whereineach of said blades has a radial length and is formed such that a ratioof an effective contact width of said blade with said conical surface tosaid radial length is no greater than a coefficient of friction betweeneach of said plurality of blades and the tool.
 15. The tool receiver ofclaim 14, wherein the dimensions of said blades satisfy the equation: D₁ /D ₂ <f; wherein D₁ is the distance between a point of contact of saidblade to the tool and a straight line between a pivot point of saidblade at said conical surface and a tool center line; D₂ is the radialdimension from the point of contact to the pivot point; and f is thecoefficient of friction between said blade and the tool.
 16. A toolreceiver for non-rotatably securing a tool to a driving device, saidtool receiver comprising: a plurality of blades, each of said pluralityof blades having a tool engaging surface and a cone engaging surfaceopposite said tool engaging surface; a conical member at least partiallyencasing said plurality of blades and biasing said plurality of bladesradially inwardly, said conical member defining a conical surface havinga narrow end and a wide end opposite the narrow end, said conical memberbeing rotatably drivable by the driving device, said plurality of bladesbeing positionable in a generally circular manner within said conicalmember whereby said tool engaging surfaces of said plurality of bladesdefine a generally circular opening, said cone engaging surfaces of saidblades engaging said conical surface of said conical member; and abiasing member which biases said blades toward said narrow end of saidconical surface such that said blades are biased in a retaining positionby said biasing member and said conical member and are adapted tonon-rotatably secure a tool with respect to said blades and said conicalmember at said tool engaging surfaces, wherein each of said plurality ofblades has a width and a radial length, a ratio of said width to saidradial length being no greater than a coefficient of friction betweensaid plurality of blades and the tool.
 17. The tool receiver of claim16, wherein said blades are pivotable within said conical member withrespect to the tool and said conical member, said tool engaging surfacesbeing engagable with the tool while said cone engaging surfaces engagesaid conical member, thereby limiting pivotal movement of said pluralityof blades relative to said conical member and further limiting rotationof the tool relative to said plurality of blades.
 18. The tool receiverof claim 17 further including a retaining member which retains saidblades in the generally circular manner within said conical member, saidretaining member being flexible to allow pivotal movement of saidblades.
 19. The tool receiver of claim 16 further including a retainingmember, said plurality of blades being interconnected by said retainingmember, said retaining member biasing said plurality of blades radiallyoutwardly toward said conical member.
 20. The tool receiver of claim 19,wherein said biasing member is releasable to allow said blades to movetoward said wide end of said conical surface, said retaining memberbiasing said blades radially outwardly whereby said tool engagingsurfaces define a larger opening for receiving a tool therein when saidbiasing member is released.
 21. The tool receiver of claim 20, whereinsaid biasing member is releasable via a lever which is movable toovercome the biasing force of said biasing member.
 22. A tool receiverfor non-rotatably securing a tool to a driving device, said toolreceiver comprising: a plurality of blades, each of said plurality ofblades having a tool engaging surface and a cone engaging surfaceopposite said tool engaging surface; a conical member at least partiallyencasing said plurality of blades and biasing said plurality of bladesradially inwardly, said conical member defining a conical surface havinga narrow end and a wide end opposite the narrow end, said conical memberbeing rotatably drivable by the driving device, said plurality of bladesbeing positionable in a generally circular manner within said conicalmember whereby said tool engaging surfaces of said plurality of bladesdefine a generally circular opening, said cone engaging surfaces of saidblades engaging said conical surface of said conical member; and abiasing member which biases said blades toward said narrow end of saidconical surface such that said blades are biased in a retaining positionby said biasing member and said conical member and are adapted tonon-rotatably secure a tool with respect to said blades and said conicalmember at said tool engaging surfaces, wherein each of said blades has aradial length and is formed such that a ratio of an effective contactwidth of said blade with said conical surface to said radial length isno greater than a coefficient of friction between each of said pluralityof blades and the tool.
 23. The tool receiver of claim 22, wherein thedimensions of said blades satisfy the equation: D ₁ /D ₂ <f; wherein D₁is the distance between a point of contact of said blade to the tool anda straight line between a pivot point of said blade at said conicalsurface and a tool center line; D₂ is the radial dimension from thepoint of contact to the pivot point; and f is the coefficient offriction between said blade and the tool.
 24. A tool receiver adaptedfor mounting to a rotational driving device and for non-rotatablysecuring a tool therewithin, said tool receiver comprising: a pluralityof blades, each of said plurality of blades having a thickness and aradial length extending radially from a generally circular openingdefined by said plurality of blades; and a conical member which isadapted to be rotatably driven by a driving device, said conical memberat least partially encasing said plurality of blades and biasing saidplurality of blades radially inwardly such that when a tool ispositioned at least partially within said opening defined by saidplurality of blades, said plurality of blades engage said conical memberand the tool, a ratio of said thickness to said radial length being nogreater than a coefficient of friction between each of said plurality ofblades and the tool.
 25. The tool receiver of claim 24, wherein saidblades contact said conical member along an effective contact width asthe driving device is operated, a ratio of an effective contact width tosaid radial length being no greater than a coefficient of frictionbetween each of said plurality of blades and the tool.
 26. The toolreceiver of claim 25, wherein the dimensions of said blades satisfy theequation: D ₁ /D ₂ <f; wherein D₁ is the distance between a point ofcontact of said blade to the tool and a straight line between a pivotpoint of said blade at said conical member and a tool center line; D₂ isthe radial dimension from the point of contact to the pivot point; and fis the coefficient of friction between said blade and the tool.
 27. Thetool receiver of claim 24 further including a biasing member whichbiases said blades in an engaging position whereby said blades areadapted to non-rotatably retain the tool within said conical member. 28.The tool receiver of claim 27, wherein said biasing member is releasableto allow said blades to move from the engaging position to a receivingposition whereby said blades are spaced to receive a tool.
 29. The toolreceiver of claim 27 further including a retaining member which retainssaid blades within said conical member, said retaining member biasingsaid blades radially outwardly toward said conical member.
 30. The toolreceiver of claim 24, wherein said blades engage said conical memberalong a cone engaging surface which is tapered to cooperate with saidconical member as said blades pivot during operation of the drivingdevice.